1. Field of the Invention
The present invention relates to a call accommodation system for accommodating calls in the order from the highest priority level.
2. Description of the Related Art
Generally, in a local area network in which video, control data, voice, etc. are collectively processed in a factory, etc., communications are established using such media as a narrow bandwidth voice, control data. etc. However, if an accident arises in a factory, etc., for example, it may be required that an emergent call should be immediately issued using a voice or a video.
FIG. 1 shows a conventional call accommodation system for accommodating calls generated as described above.
In FIG. 1, A, B, C, and D are nodes, and a fine arrow between the nodes indicates a capacity of the transmission line, for example, 10, connecting the nodes. A bold line with an arrow on one end indicates a bandwidth of an existing call to be transmitted from one node to another.
Assuming that communications are established from node A to node B, a communications line from node A to node B can be a direct circuit A.fwdarw.B, or a detour circuit A.fwdarw.C.fwdarw.B or A.fwdarw.D.fwdarw.B. Assume that an emergent call designated bandwidth 7 has been issued from node A to node B, a destination.
First, in this case, direct circuit A.fwdarw.B is checked for available bandwidths. If, for example, existing calls 2 and 3 are detected as being designated bandwidths 2 and 3, respectively, in direct circuit A.fwdarw.B, then an emergent call designated bandwidth 7 cannot be accommodated in direct circuit A.fwdarw.B.
Then, detour circuits A.fwdarw.C.fwdarw.B and A.fwdarw.D.fwdarw.B are checked for available bandwidths. In detour circuit A.fwdarw.C.fwdarw.B, if existing calls designated bandwidths 3 and 4 are separately detected in circuit A.fwdarw.C, and an existing call designated bandwidth 3 is detected in circuit C.fwdarw.B, then an emergent call designated bandwidth 7 cannot be accommodated in detour circuit A.fwdarw.C.fwdarw.B. On the other hand, if an existing call designated band 3 is detected in circuit A.fwdarw.D and an existing call designated bandwidth 2 is detected in circuit D.fwdarw.B in detour circuit A.fwdarw.D.fwdarw.B, then an emergent call designated bandwidth 7 can be accommodated in detour circuit A.fwdarw.D.fwdarw.B.
Thus, the emergent call designated bandwidth 7 is finally accommodated in detour circuit A.fwdarw.D.fwdarw.B.
At this time, if the existing call designated is equal to or larger than bandwidth 1 is detected in addition to the existing call designated bandwidth 3 in circuit A.fwdarw.D, then the emergent call designated 7 cannot be accommodated in detour circuit A.fwdarw.D.fwdarw.B, either. Accordingly, the emergent call designated bandwidth 7 cannot be accommodated in any circuit from node A to node B, and the call is rejected.
To prevent an emergent call from being rejected in the above described conventional method, available bandwidths must be necessarily reserved for an emergent call either in a direct circuit or a detour circuit. In the example shown in FIG. 1, ten or more trunk capacity should be reserved in either a direct circuit or a detour circuit between nodes A and B.
However, all reserved bandwidths are not occupied in the above described conventional call accommodation system, thus the reservation results in an inefficient utilization and there is an increase in cost of a circuit.
However, limiting the reservation of the bandwidth to the smallest possible extent often causes an emergent call to be rejected undesirably.